STUDY DETAILS
DISTRIBUTION, IMPACTS OF CARBON DIOXIDE IN THE WORLD OCEANS

An international team of scientists has
completed the first comprehensive study of the ocean storage of carbon
dioxide derived from human activity based on a decade-long survey
of global ocean carbon distributions in the 1990s.

The global survey combined measurements
of carbon and other ocean factors such as temperature, salinity, oxygen,
nutrients and chlorofluorocarbon tracers in the Atlantic, Pacific
and Indian oceans to determine that the oceans have taken up about
118 billion metric tons of carbon dioxide from human sources (anthropogenic
CO2) between 1800 and 1994. This is approximately a third of its long-term
potential.

These findings, plus a companion paper
on the impacts of anthropogenic CO2 on the chemistry of the oceans
and the potential response of certain marine species to the changes
in CO2 levels, will be published in the July 16 issue of the journal
Science. Lead authors for both papers are scientists with the Commerce
Department’s National Oceanic and Atmospheric Administration.

Analysis of CO2 levels in ice cores have
shown scientists that for the 400,000 years before the industrial
revolution began in the 1800s, atmospheric CO2 concentrations remained
between 200 and 280 parts per million. Today CO2 levels are reaching
380 parts per million in the atmosphere.

“If the ocean had not removed 118
billion metric tons of anthropogenic carbon between 1800 and 1994,
the CO2 level in the atmosphere would be about 55 parts per million
greater than currently observed,” said Christopher Sabine an
oceanographer at the NOAA’s Pacific Marine Environmental Laboratory
in Seattle, Wash., and the lead author of one of the papers.

Because the ocean mixes slowly, the anthropogenic
CO2 from the atmosphere is generally confined to the upper layers
of the ocean.

“About half of the anthropogenic
CO2 taken up over the last 200 years can be found in the upper 10
percent of the ocean. The ocean has removed 48 percent of the CO2
we have released to the atmosphere from burning fossil fuels and cement
manufacturing,” Sabine said.

Sabine
and his colleagues from the United States, South Korea, Australia,
Canada, Japan, Spain, and Germany reviewed data gathered during the
1990s as part of three major research programs: the World Ocean Circulation
Experiment, the Joint Global Ocean Flux Study and NOAA’s Ocean-Atmosphere
Carbon Exchange Study.

This new global data set of ocean-carbon
system observations, co-sponsored in the United States by NOAA, National
Science Foundation and Department of Energy, is unprecedented with
more than 72,000 carbon measurements, 10 times more observations than
the previous global survey in the 1970s and 10 times more accurate.

"This research presents the first
complete synthesis of modern global ocean inorganic carbon measurements,"
said James Yoder, director of NSF's ocean sciences division.

There are two large reservoirs of carbon
that are capable of taking significant amounts of CO2 out of the atmosphere:
the ocean and land plants. Studies over the last decade have indicated
that the land plants are taking up CO2 at rates comparable to the
oceans. The new high quality ocean carbon measurements allow scientists
to determine that over a 200-year time-scale, the land plants have
released more CO2 to the atmosphere than they have taken up. Over
the long-term, therefore, the ocean has been the only reservoir to
consistently take up anthropogenic CO2 from the atmosphere.

The uptake of anthropogenic CO2 by the ocean changes its chemistry
and potentially can have significant impacts on the biological systems
in the upper oceans.

Richard Feely, a marine chemist with
NOAA's Pacific Marine Environmental Laboratory, and colleagues describe
two major impacts of the oceanic uptake of anthropogenic CO2. First,
they demonstrated that a substantial amount of the calcium carbonate
shells produced in surface waters dissolves in the upper ocean. Second,
they summarized the available evidence on the response of marine calcifying
organisms to elevated CO2.

Feely noted that scientists have seen
a reduced ability to produce protective calcium carbonate shells in
many species of marine organisms at high CO2 levels, including corals
and free-swimming algae (plant-like organisms) and animals on which
other marine life feed. Recent studies have shown that calcification
rates can drop by as much as 25 to 45 percent at CO2 levels equivalent
to atmospheric concentrations of 700 to 800 parts per million that
will be reached by the end of the century if fossil fuel consumption
continues at projected levels.

The scientists note that the dissolving
calcium carbonate shells also partially act to neutralize the CO2,
thus allowing the ocean to take up more carbon dioxide from the atmosphere.
However, the effects of decreased calcification in microscopic algae
and animals could alter marine food webs and, combined with other
changes in salinity, temperature and upwelled nutrients, could substantially
alter the diversity and productivity of the ocean.

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